With the rapid development of wireless communication technologies, wireless terminals such as mobile terminal or data card receive widespread application; it also can be found that the size of the wireless terminal gets smaller and smaller; while the design difficulty of the wireless terminal structure is increased, another important problem is caused too, that is, electromagnetic radiation of the wireless terminal on a human body is enhanced.
At present, the index to measure the electromagnetic radiation of an antenna on a human body is SAR, which refers to a specific absorption value of the electromagnetic energy of the wireless terminal; the specific implication is that: by the action of external electromagnetic field, an induction electromagnetic field is generated inside a human body; since each organ inside the human body is lossy dielectric, the electromagnetic field inside the human body generates induced current which then causes the human body to absorb and dissipate electromagnetic energy; the SAR is usually used to represent this physical process in biological dosimetry. The implication of SAR refers to the electromagnetic power absorbed or dissipated by human tissue per unit mass, wherein the unit is W/kg or mW/g; the federal communications commission (FCC) of united states definitely regulates the maximum allowed SAR during the interaction of each kind of wireless terminal and a human body; the FCC also regulates that the SAR of the mobile terminal should be measured when the mobile terminal approaches one side of the human brain; the SAR of the data card must be measured on four sides near the data card antenna. Therefore, the point how to meet the electromagnetic radiation standard of the human body while the wireless terminal is miniaturized has become the important problem to be solved immediately.
At present, the wireless terminal SAR attenuation technology, that is, the SAR peak attenuation technology, usually is to coat a wave-absorbing material and/or an anti-radiation layer on the surface of the wireless terminal housing, but the production cost is high; besides, there is a method for setting a conductor reflector and a shielding device in the wireless terminal, thus, during the assembly process of the wireless terminal, it is necessary to provide corresponding location space for the conductor reflector and the shielding device, and more space is occupied; therefore, the original purpose of wireless terminal miniaturization design is violated.
Although both the two solutions above can reduce the SAR, the two solutions have a common defect, that is, after a wave-absorbing material and/or an anti-radiation layer is coated on the surface of the wireless terminal housing, although the coated wave-absorbing material and/or the anti-radiation layer absorbs the electromagnetic wave radiated on the human body by the wireless terminal, the coated wave-absorbing material and/or the anti-radiation layer also absorbs the useful signal radiated outwards in a form of electromagnetic wave by the antenna, thus the communication quality of the wireless terminal is influenced; similarly, although the conductor reflector and the shielding device can isolate the electromagnetic wave radiated on the human body, the conductor reflector and the shielding device also can isolate the signal useful signal radiated outwards by the antenna, thus the communication quality of the wireless terminal is influenced. By the two solutions above, while the SAR of wireless terminal is reduced, the communication performance of the wireless terminal is influenced too, that is to say, the radiation of the near region of the wireless terminal antenna on the human body is reduced, however, the far-field radiation of the antenna is influenced greatly and the wireless terminal can not communicate successfully, thus communication quality can not be guaranteed.